Sex—one small word with huge implications. To most humans, being male or female implies a certain set of inseparable biological and sociological characteristics, but the natural world around us is rarely so black and white. For every characteristic that we associate with a particular sex, the animal kingdom harbors at least one surprising exception; concepts that we believe are inextricably linked are uncoupled, and even reversed, in other species.

Our sex exerts an incredible influence on our lives, influencing anatomy, appearance, behavior, and countless other traits. Socially, our sex also matters in terms of how we are understood and treated by others, because we see each other through a gendered lens. Female college graduates are hired more often than male graduates, for instance, but earn 17 percent less than their male counterparts. Police pull male drivers over at a much higher rate than they do female drivers. In high school math classes, teachers direct questions toward, call on, and interact with male students much more frequently than females.

We tend to recognize differences between males and females and try to explain them as a function of sex; we classify some things as masculine and others as feminine, often couching these divisions in evolutionary terms. But these justifications are often inaccurate. As we'll see below, many of the sociological differences between males and females have little, if any, universal relationship to sex.

“Sex” vs. “gender”

Most humans make no real distinction between the words “sex” and “gender”—one term often replaces the other. When asking about a friend’s pregnancy, we might ask about either the sex or the gender of the baby with the same intent, and the US Census Bureau even uses the words “sex” and “gender” interchangeably. The general confusion between these terms made headlines recently when a transgender contestant wanted to compete in the Miss Universe Pageant; a kerfuffle ensued when nobody could quite figure out if that should be allowed.

Sex is a scientific concept, referring to the biological and physiological differences between males and females. In humans, males have penises, an X and a Y chromosome, and generally lower voices and higher amounts of body hair. Vaginas, two X chromosomes, and the ability to lactate and to menstruate are sex characteristics usually belonging to females. These traits aren’t universal in males and females of other species, but they are representative of the biological concept of sex.

Gender, meanwhile, is a sociological construct. Most often, the term “gender” describes how men and women fulfill certain cultural norms defined by their sex. The World Health Organization says that gender “refers to the socially constructed roles, behaviors, activities, and attributes that a given society considers appropriate for men and women.” Gender encompasses everything from preferences to hobbies to roles in the home and the workplace, and the term applies only in a human context; since it is a social concept, gender does not apply to other species.

That's not to say that cultural gender roles have no roots in biology. The tendency for women to take on many of the parental duties, for example, likely stems from mothers’ ability to lactate, providing necessary nourishment for their children. Biologically, men are drawn to a woman’s hourglass figure because it signals health and fertility; many women, in turn, try to alter or enhance their body shape to fulfill this standard of beauty.

However, ties to biology are not necessary for gender roles to develop, and many of these roles have nothing at all to do with sex. For instance, we often associate girls with pink and boys with blue. But it was standard in the US during the early 1900s to dress American boys in pink and girls in blue. With its hint of "powerful" red, pink was considered a “stronger” color, while blue was thought to be “daintier” and more suitable for girls. These preferences changed in the mid-20th century; today, many parents wouldn’t dare dress their sons in pink.

Because gender roles are so pervasive in human culture, we tend to use them to help us understand the rest of the world. Unfortunately, viewing nature through a human lens doesn’t always give us an accurate picture of what is going on. Nature constantly engineers new and creative solutions to all sorts of problems—turning our stereotypes about sex upside-down along the way.

Appearances can be deceiving

The spotted hyena may have one of the most arresting sexual incongruities in the animal kingdom. Female hyenas possess what scientists call "pseudopenises," since they so closely mimic male penises. These female organs are fully erectile, can be up to seven inches long, and are accompanied by a “pseudoscrotum.” Stranger still, a female hyena must urinate, copulate, and give birth through her pseudopenis. No wonder that, for centuries, people thought hyenas were hermaphrodites—watching a mom with a large penis nurse her babies can be a little confusing.

In a different kind of genital reversal, many males in the animal kingdom lack a penis entirely. In more than 97 percent of bird species, males have no external sex organ at all; instead, both males and females have vents called "cloacas." In these species, mating involves the romantic-sounding “cloacal kiss,” where the two birds line up their genital vents for the transfer of sperm.

We generally expect the males of a species to be big and burly, but biologically speaking, it doesn’t always pay for males to be larger than females. In some spider species, for instance, the females are much larger than males. Researchers believe that this is due to the males’ need to move around efficiently, as lightweight males can better scamper across “bridges” to get from place to place and spread their genes.

In other species, being large provides a definite advantage for females. Sometimes referred to as the BOFFFF ("Big Old Fat Fecund Female Fish”) hypothesis, the idea builds on the fact that large females can carry and spawn an exponentially greater number of eggs than smaller females. Since sending more offspring out into the world is a huge biological advantage for these females, larger bodies are favored, and these species have little or no similar selection pressure for large males.

Males are often the showier sex, of course; male deer have elaborate antlers, male lions have huge manes, and most male birds and fish are more colorful than their female counterparts. But little about appearance is a constant. In a species called the empedid dance fly, for instance, females are actually the sex with flashier signals. While male dance flies are unadorned, the females have “ornaments” on their abdomens and legs that may trick males into thinking that the female's eggs are more mature that they really are. But these adornments, like many of the male sex ornaments, are costly—they make it much harder for females to escape from spider webs.

Your entertaining list of trivia really doesn't support this specific claim of yours. What is instead says is that sexual roles vary from species to species. That species differ from each other isn't all that complicated.

Your list doesn't even support your argument for defining 'sex' as being a marker for biological/physical features and 'gender' as being a marker for behavioral features. You and some professionals may prefer to distinguish the terms in that way, but clearly, most people do not. So by the norms of language, sex is synonymous with gender, regardless of what you may think. This doesn't really present a semantic problem either. Saying that sexual roles differ between species is no more or less clear than saying that gender roles differ between species.

Out of 104 papers, only 5 percent defined the term “sex,” just 6 percent defined the term “gender,” and nearly 40 percent used the two terms interchangeably. When researchers don’t bother—or even worse, avoid—defining terms in their own field, there’s a definite problem in our understanding of these concepts.

I appreciate the need for scientists to use their terminology correctly, but it should not be necessary and isn't especially common for basic terms with agreed upon meanings to be defined in every paper. The 40% statistic is disturbing, but for those papers that use "sex" and "gender" properly (especially in situations where only one or the other is discussed), repeating definitions of precise but nuanced terminology just wastes space in what is often a severely limited page count.

You and some professionals may prefer to distinguish the terms in that way, but clearly, most people do not. So by the norms of language, sex is synonymous with gender, regardless of what you may think. This doesn't really present a semantic problem either.

"Most people" are not scientists studying human and animal sexual characteristics. What "most people" call it is irrelevant to science.

"Most people" call small dots of light in the sky stars, but some are planets or other phenomena. We would not want astronomers to insist on calling Venus a star just because linguistically the average person refers to anything up there as a star. The average person engaged in this behavior is still wrong even through they have lots of company.

Your entertaining list of trivia really doesn't support this specific claim of yours. What is instead says is that sexual roles vary from species to species. That species differ from each other isn't all that complicated.

Your list doesn't even support your argument for defining 'sex' as being a marker for biological/physical features and 'gender' as being a marker for behavioral features. You and some professionals may prefer to distinguish the terms in that way, but clearly, most people do not. So by the norms of language, sex is synonymous with gender, regardless of what you may think. This doesn't really present a semantic problem either. Saying that sexual roles differ between species is no more or less clear than saying that gender roles differ between species.

It's pretty common for scientific terminology to have a more nuanced but precise definition than what the general population uses. For a quick example, "mass" and "weight" have extremely different meanings to a scientist or an engineer, but are used completely interchangeably by the general public.

Nor, I think, is the list supposed to justify the distinction between sex and gender - words are inherently not natural. "Sex" has been defined in the biological community as the physiological state of being male or female, while "gender" is the social construct that's built up around particular sexes. These distinctions are made by people, for people (scientists mainly) so that they can clearly talk about these separate concepts with separate words. It's only a pity that even the scientists in the field are too lazy to be consistent and precise with their language.

Your entertaining list of trivia really doesn't support this specific claim of yours. What is instead says is that sexual roles vary from species to species. That species differ from each other isn't all that complicated.

thought it was fine. the lesson is that we can't apply the understanding of ourselves to the rest of the animal kingdom.

Interesting point on the smaller male spiders, but for a number of families the small males seem to have evolved because they're less likely to be eaten by the females they're trying to get it on with =)

We generally expect the males of a species to be big and burly, but biologically speaking, it doesn’t always pay for males to be larger than females.

QFT. In nutrient poor environments, it pays for individuals to grow large (having a buffer against starvation). But anglerfish males do well as diminutive integrated symbionts. [ http://en.wikipedia.org/wiki/Anglerfish ]

It's in the science section. We've had a science section for as long as I've been at Ars.

It also fits nicely with the so-called "liberal agenda" of Ars.

Science is funny that way: on the one hand it mainly supports fiscal conservatism, capitalism and the free market (supports, as in: estimates these are better at reaching their avowed goals than their alternatives), on the other hand, it proves that all the hoopla about creationism/ID, "natural" sexual/gender behaviours,... is just bunk.

Why people often accept one but not the other is beyond my comprehension. I'm not sure if its idiocy, or self-serving partial blindness.

You and some professionals may prefer to distinguish the terms in that way, but clearly, most people do not. So by the norms of language, sex is synonymous with gender, regardless of what you may think. This doesn't really present a semantic problem either.

"Most people" are not scientists studying human and animal sexual characteristics. What "most people" call it is irrelevant to science.

"Most people" call small dots of light in the sky stars, but some are planets or other phenomena. We would not want astronomers to insist on calling Venus a star just because linguistically the average person refers to anything up there as a star. The average person engaged in this behavior is still wrong even through they have lots of company.

You're mistaken. Words like "star" and many others (energy, power, bit, information, gravity, et cetera) were originally used in broader, more abstract ways. They were then adopted by scientific thinkers and given a narrower, more specific definition for the purposes of science. As a result, these words have multiple definitions depending on context. The people who use them more broadly aren't wrong, they are using a different (and frequently older) definition.

Which is exactly why it might be good practice in papers to specify exactly which definition one is using, if the term may potentially be ambiguous. I think the relationship between sex and gender is poorly understood enough to warrant clarification.

In a different kind of genital reversal, many males in the animal kingdom lack a penis entirely. In more than 97 percent of bird species, males have no external sex organ at all; instead, both males and females have vents called "cloacas." In these species, mating involves the romantic-sounding “cloacal kiss,” where the two birds line up their genital vents for the transfer of sperm.

Of course this "difference" isn't for the sake of being different, but that external sex organs may increase drag, and represent something that may impede movement. Nature if nothing else is practical in the larger context that each animal occupies.

It's in the science section. We've had a science section for as long as I've been at Ars.

It also fits nicely with the so-called "liberal agenda" of Ars.

Because conspiracy theories fits a science blog. (O.o)

Science is as much liberal as it is atheist, but relatively so: is is because conservatives often prefer to deny science as much as they can get away with. (Sex biology denial, climate science denial, et cetera.)

On top of that there is a liberal skew because top scientists are liberal nearly as much as they are atheist, or at least I think that is what the statistics says. The reasons for this is much more complicated than, say, atheism. But one reason is likely because science push the envelope that conservatives aren't comfortable with.

Biologically sex is relative a species, fetuses aren't alive, human females is indistinct from males, and gender is a social construct.

It's in the science section. We've had a science section for as long as I've been at Ars.

It also fits nicely with the so-called "liberal agenda" of Ars.

Science is funny that way: on the one hand it mainly supports fiscal conservatism, capitalism and the free market (supports, as in: estimates these are better at reaching their avowed goals than their alternatives), on the other hand, it proves that all the hoopla about creationism/ID, "natural" sexual/gender behaviours,... is just bunk.

Why people often accept one but not the other is beyond my comprehension. I'm not sure if its idiocy, or self-serving partial blindness.

The interesting part is that most people accept one or the other, but not both. But then again, perhaps it's because science doesn't necessarily prove anything. It's hard to say that we as humans should implement a completely capitalistic society, even if it would seem to be the best. It's hard to say that science disproves ID, because it can't say that something of intelligence didn't play a role in where we are now. As far as natural behaviors, I agree that claiming something is right/wrong because animals do it is clearly odd. However, that doesn't necessarily mean something is/isn't natural for one species.

Of course this "difference" isn't for the sake of being different, but that external sex organs may increase drag, and represent something that may impede movement. Nature if nothing else is practical in the larger context that each animal occupies.

The reason generic birds use the cloacal kiss is because the dinosaur clade has likely always used it. http://www.wired.com/wiredscience/2012/ ... n-dinosex/ : "Everyone is agreed that male dinosaurs mounted females, most likely from behind, so that the pair could bring their cloacal openings into contact."

This is an interesting article, and I look forward to reading the future installments, but I have reservations about the premise that looking at animal sex can illuminate human sex. Sex is cultural-- the act is, really, mechanical and insignificant. As is the hardware, when you get down to it. Obviously a lot more goes into it when people get together. So what can science tell us about culture and human nature? Not much, from my experience. It can tell us the what but not the why-- not ultimately. People have tried to apply science and reason to society at least since the ancient Greeks, and the world is still screwed up. I don't mean to ramble (I will anyway), but I'm always skeptical when science tries to understand human nature, because scientists being natural problem solvers, it always ends up coming to the question of human perfectibility. Cold reason tends to create monsters. There's messiness and mystery at the center of us. It's something the mind will never master. That's why we have the arts and humanities.

Anyway, I started to say all of this because of the question of liberal bias and got off track... sometimes what appears as an agenda is simply the consequence of seeing the world in a particular way. Writing and publishing what interests you (and your audience) isn't automatically an ideological assault.

Science is funny that way: on the one hand it mainly supports fiscal conservatism, capitalism and the free market (supports, as in: estimates these are better at reaching their avowed goals than their alternatives), on the other hand, it proves that all the hoopla about creationism/ID, "natural" sexual/gender behaviours,... is just bunk.

Why people often accept one but not the other is beyond my comprehension. I'm not sure if its idiocy, or self-serving partial blindness.

I'll bite.

Economics science does not support fiscal conservatism as a "good" system. "Good" is inherently subjective. "Good" can mean equitable distribution of resources, the greatest sum consumption of resources, the preservation of resources for future generations, the greatest happiness per capita, or a dozen different thing, all of which would imply wildly different best system. The best economics can hope to do is inform on the consequences and let you know if your actions are going to take you closer to whatever "good" you are aiming for.

To make matters worse, broad economic systems are violently chaotic systems with quickly changing rules that make climate systems look dull. You can get some consensus on microeconomics and consensus on a few rough rules for macroeconomics, but as soon as you start getting into details the knives come out. Tell a group of economist that the "good" you want is high employment and an end to an economic downturn, and the Keynesian and Austrians Schools will promptly pull out knives in violent disagreement and a blood bath will result.

Your entertaining list of trivia really doesn't support this specific claim of yours. What is instead says is that sexual roles vary from species to species. That species differ from each other isn't all that complicated.

Your list doesn't even support your argument for defining 'sex' as being a marker for biological/physical features and 'gender' as being a marker for behavioral features. You and some professionals may prefer to distinguish the terms in that way, but clearly, most people do not. So by the norms of language, sex is synonymous with gender, regardless of what you may think. This doesn't really present a semantic problem either. Saying that sexual roles differ between species is no more or less clear than saying that gender roles differ between species.

It's pretty common for scientific terminology to have a more nuanced but precise definition than what the general population uses. For a quick example, "mass" and "weight" have extremely different meanings to a scientist or an engineer, but are used completely interchangeably by the general public.

Nor, I think, is the list supposed to justify the distinction between sex and gender - words are inherently not natural. "Sex" has been defined in the biological community as the physiological state of being male or female, while "gender" is the social construct that's built up around particular sexes. These distinctions are made by people, for people (scientists mainly) so that they can clearly talk about these separate concepts with separate words. It's only a pity that even the scientists in the field are too lazy to be consistent and precise with their language.

That seems like a good example. For most people, mass and weight are functionally interchangeable, since they deal only with circumstances of constant gravity. Likewise, I think it's fair to say that most people do not encounter circumstances where sex and gender do not align. So it's not surprising the words are often swapped. For both pairs of words, that doesn't mean it's correct to use them interchangeably.

Female jacanas…mate promiscuously… [but it's] the male’s job to incubate the eggs and care for the young

Anybody who can suggest how this behavior got selected by evolutionary pressures is welcome to suggest it.

Perhaps it keeps the males in the female's territory were she can control access to them. From a genetic standpoint the role of polyandry (one female with several male mates) could be the reverse of polygyny (one male with several female mates). Instead of ensuring that all the offspring share the father's genes, a polyandrist species of bird could ensure that the offspring of a single female have multiple fathers, and therefore a wider assortment of genes to improve the chances that some will make it to adulthood and pass on the mother's genes. In species without much sexual dimorphism (i.e. where there's not much difference between males and females) and not a long period of gestation, the sex of the parent giving care is less important than in mammals (where there's an obvious incentive for females to be the caregivers). If it starts to become important again for some reason, there might be nothing stopping the female from taking on the "traditionally" male role of dominating a territory and a harem of mates.

Other examples of human parental gender role reversals can be found in familiar fish. Fathead minnows (usually available in a bright orange strain called "Rosy Reds" from your bait shop) have a male that aggressively protects and takes care of the eggs once they're laid by one or more females under a rock or log. If he didn't chase off the females that laid the eggs, she'd eat them. Male bettas are also the nest builders and caregivers in their species.

Female jacanas…mate promiscuously… [but it's] the male’s job to incubate the eggs and care for the young

Anybody who can suggest how this behavior got selected by evolutionary pressures is welcome to suggest it.

I'm not certain every observed behavior must be accounted for in terms of direct selection pressure. One has to explain a moth's spiral into a candle-flame in terms of a mis-firing of its navigation system (presumably), for example; not as an example of selected-for suicide. I'm not suggesting that there isn't a valid natural slection pressure for most observed behaviors but rather that the direct line from selection pressure to behavior is often surprising.

For a greatly entertaining and informative treatment of the subject, be sure to check out Olivia Judson's "Dr. Tatiana's Sex Advice to All Creation". It's a rare book that can make me both laugh out loud and marvel at how little most of us know about life on Earth.

A more serious, but equally entertaining book focused on the evolution of human sexuality specifically is Christopher Ryan and Cacilda Jethá's "Sex at Dawn".

Fascinating stuff that will likely change, or at least make you pay closer attention to, things most of us take for granted as being obvious.

It's in the science section. We've had a science section for as long as I've been at Ars.

It also fits nicely with the so-called "liberal agenda" of Ars.

Most of the world doesn't conform to the US's retarded political system where your choices are between ultra conservative and highly conservative.

In the real world most developed countries consider what you call 'liberal' to be the centre ground of politics and acknowledge scientific discoveries instead of creating false controversies with pseudo-religious hypotheses. I guess though your better than totalitarian regimes and religious theocracies to if you set the bar low enough I can manage a sarcastic "well done!".

Now back to the article at hand and ignoring the off-topic rubbish about if this article belongs on this site.

All I can say is please can we have more of this!

I want interesting, in depth reportage. There has been far too many articles regurgitating PR announcements or time wasting speculation (basically most of the Apple section) and I've lately been disappointed that so much time is spent on this rather than in depth reviews and interesting articles. At this point, the few interesting reviews and science output are what still make Ars worth coming to (also I've really appreciated the increased focus on security issues). The other time wasting stuff can be found on Engadget, etc. and to be frank they're quicker and better at that stuff than you are. I'm sure it comes down to pageviews at the end of the day, but you could easily jettison the entire Apple section and smartphones and tablets in general (although still offer good in depth reviews of their products) and maybe do a daily or weekly roundup of notable product announcements. This would greatly increase the signal to noise ratio of the site although I appreciate it would be bad for your advertising revenues!

Have there been any transgender persons who wanted to get a persistent cloaca installed because they thought they should have been born with one? Or is it always among the familiar male/female organs (or lack thereof)?

'"As we'll see below, many of the sociological differences between males and females have little, if any, universal relationship to sex."

Sorry but this is simply nonsense. Most mammals do conform to the "sociological difference between males and females" and it is tied to sex. Are there exceptions? Yes, of course there are. But exceptions do not invalidate what are universal trends. The same is generally true of primates.

Finally since the OP insists on inserting humans in the discussion, anyone who thinks humanity developed apart from these sociological differences or that these were not tied to sex is trying to proves something that just cant be shown.

I really don't see what the point of all this is anyway. Our rights, our ability to make choices for ourselves of how we want to live; these have nothing to do with biology or sex.

It's pretty common for scientific terminology to have a more nuanced but precise definition than what the general population uses. For a quick example, "mass" and "weight" have extremely different meanings to a scientist or an engineer, but are used completely interchangeably by the general public.

"Sex" has been defined in the biological community as the physiological state of being male or female, while "gender" is the social construct that's built up around particular sexes. It's only a pity that even the scientists in the field are too lazy to be consistent and precise with their language.

Your last sentence undermines your point that "sex" and "gender" are used differently by life scientists. Some industry body may have come up with a definition, but if that definition is not policed, it's not very useful.

In contrast, if you misuse mass/weight in a journal paper, the peer reviewers will smack you down for it.

Sorry but these types of articles are mostly pointless unless you're an evolutionary biologist or something. But since this is really an article aimed at creating a social message from anecdotal data from the animal kingdom, who is it for?

Anyone with an open mind towards accepting people with non-traditional sexuality aren't in need of convincing that "it's OK because animals do weird shit too", and the narrow-minded rednecks who think it's deviant behavior aren't suddenly going to say "Look here Mirna, says Hyenas have fake dicks and hump each other! I guess being gay is OK!"

More like"Hyenas are what happen when dog species mate with cat species and created a ruined form of sodomist devils! It's God's punishment that they all have to grow dicks and hump either other in the eternal hell-fires of teh Okavango!"

Sex is a scientific concept… Gender, meanwhile, is a sociological construct.

Sex, from sexus, division, gender, possibly from seco, cut off, cleave, divide. Gender, from genus, kind, race, kin. The idea of sex as biology and gender as a role came from John Money in 1955, but the word gender was used in the biological sense since at least the 15th century, whereas sex was first used in that sense in the 16th century. Furthermore, Money's distinction never completely eliminated what he considered "improper use", so arguing that "sex" should be used in place of "gender" in the biological sense is not only pointless but wrong.

Kate Shaw Yoshida / Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas.